Period Limitation for Using the cBathy

[lalafreguete]

Good afternoon. I am trying to apply the cBathy methodology for Texas areas, but the wave average period here is shorter than 10 s. Is this a problem for the use of cBathy? Does the algorithm has a period inferior limit where it can not solve the frequency?

Thank you.

[bergsmaE]

Actually, the code has been developed on wave periods like that, rather than long period swells. Also you have more spectral “period” resolution around the shorter wave period. In short, shouldn’t be any problem :-) ,a priori, based on the period.

There is tons of other factors that could make it not to work.

Cheers,

Erwin

On 30 Nov 2020, at 21:45, lalafreguete notifications@github.com wrote:



Good afternoon. I am trying to apply the cBathy methodology for Texas areas, but the wave average period here is shorter than 10 s. Is this a problem for the use of cBathy? Does the algorithm has a period inferior limit where it can not solve the frequency?

Thank you.

— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHubhttps://github.com/Coastal-Imaging-Research-Network/cBathy-Toolbox/issues/62, or unsubscribehttps://github.com/notifications/unsubscribe-auth/AGCX3R6KU2OPWZBP6HNESHDSSP76BANCNFSM4UICVIVQ.

[RobHolman]

Good answer (thanks Erwin), although I wouldn’t likely have said “tons of other factors” could make it fail. Mostly it struggles with large wave heights. In mellow conditions (say < 1.2 m) it seems pretty robust.

YHS…Rob

Rob Holman SECNAV/CNO Chair in Oceanography

104 Ocean Admin Bldg. CEOAS-OSU Corvallis, Oregon, USA 97331-5503 ph: 1-541-737-2914 holman@coas.oregonstate.edu http://cil-www.coas.oregonstate.edu

On Nov 30, 2020, at 1:35 PM, Erwin notifications@github.com wrote:

[This email originated from outside of OSU. Use caution with links and attachments.]

Actually, the code has been developed on wave periods like that, rather than long period swells. Also you have more spectral “period” resolution around the shorter wave period. In short, shouldn’t be any problem :-) ,a priori, based on the period.

There is tons of other factors that could make it not to work.

Cheers,

Erwin

On 30 Nov 2020, at 21:45, lalafreguete notifications@github.com wrote:



Good afternoon. I am trying to apply the cBathy methodology for Texas areas, but the wave average period here is shorter than 10 s. Is this a problem for the use of cBathy? Does the algorithm has a period inferior limit where it can not solve the frequency?

Thank you.

— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHubhttps://github.com/Coastal-Imaging-Research-Network/cBathy-Toolbox/issues/62, or unsubscribehttps://github.com/notifications/unsubscribe-auth/AGCX3R6KU2OPWZBP6HNESHDSSP76BANCNFSM4UICVIVQ. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub, or unsubscribe.

[lalafreguete]

Thank you all for your inputs, gentlemen. I have used the CIRN toolbox workflow and implementing the cBathy. The results look correct, I just need to assess the resulting bathymetry with surveyed data now to see how good is the estimated depth values. Has anyone tried to compare the bathy matrix with georeferenced ground truths?

Thanks!

[KateBrodie]

Hello,

There are numerous publications documenting the accuracy of cBathy relative to nearshore surveys. The original cBathy paper, Holman et al., 2013 is a good place to start. In addition, Brodie et al., 2018 extended this analysis to a wide range of wave conditions and discussed sources of errors to be aware of. In addition there is a table in Brodie et al 2018 that lists many of the other published papers evaluating the accuracy of cBathy relative to surveyed data - some in locations with large tidal ranges or short periods, etc.

What do you hope to use your cBathy results to investigate or study?

Thanks! -Kate

[lalafreguete]

Thanks for the references! I have been used those works as my bibliographic foundation. The goal of the work is to compare the results from Sfm photo-bathymetry and cBathy results. But I believe I need to rephrase my question because I did not articulate it very well, I apologize for that. I meant to ask: how to convert the ground truth data into the cBathy local coordinate so it can be compared with the cBathy output ?

[bergsmaE]

Hi Rob,

Sorry, you’re right. I was more answering in a figure of speech that it is hard to determine/pinpoint why cBathy would struggle; given the information we have it shouldn’t necessarily.

Cheers,

Erwin

On 1 Dec 2020, at 01:46, Rob Holman notifications@github.com wrote:



Good answer (thanks Erwin), although I wouldn’t likely have said “tons of other factors” could make it fail. Mostly it struggles with large wave heights. In mellow conditions (say < 1.2 m) it seems pretty robust.

YHS…Rob

Rob Holman SECNAV/CNO Chair in Oceanography

104 Ocean Admin Bldg. CEOAS-OSU Corvallis, Oregon, USA 97331-5503 ph: 1-541-737-2914 holman@coas.oregonstate.edu http://cil-www.coas.oregonstate.edu

On Nov 30, 2020, at 1:35 PM, Erwin notifications@github.com wrote:

[This email originated from outside of OSU. Use caution with links and attachments.]

Actually, the code has been developed on wave periods like that, rather than long period swells. Also you have more spectral “period” resolution around the shorter wave period. In short, shouldn’t be any problem :-) ,a priori, based on the period.

There is tons of other factors that could make it not to work.

Cheers,

Erwin

On 30 Nov 2020, at 21:45, lalafreguete notifications@github.com wrote:



Good afternoon. I am trying to apply the cBathy methodology for Texas areas, but the wave average period here is shorter than 10 s. Is this a problem for the use of cBathy? Does the algorithm has a period inferior limit where it can not solve the frequency?

Thank you.

— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHubhttps://github.com/Coastal-Imaging-Research-Network/cBathy-Toolbox/issues/62, or unsubscribehttps://github.com/notifications/unsubscribe-auth/AGCX3R6KU2OPWZBP6HNESHDSSP76BANCNFSM4UICVIVQ. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub, or unsubscribe.

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[KateBrodie]

There is some nice documentation in the CIRN Quantitative Coastal Imaging Toolbox on local coordinate systems - if you are using that toolbox to rectify the data (which is our new recommended way) it should provide you your rectified orthophotos in both a local and global coordinate system, so you would already have the global coordinates for your cBathy grid. Check out the wiki within that repository for more information on coordinate transformations.

If you developed your own local coordinate system to run cBathy, to convert the local grid values back into global values, you would need to basically reverse your calculations. So usually you define a local origin in global coordinates and apply a translation and then have a rotation about the z-axis to rotate your x-y coordinates into local coordinates.